title: Lack of primary cilia primes shear-induced endothelial-to-mesenchymal transition.
abstract: BACKGROUND
  Primary cilia are cellular protrusions that serve as mechanosensors for fluid flow. In endothelial cells (ECs), they function by transducing local blood flow information into functional responses, such as nitric oxide production and initiation of gene expression. Cilia are present on ECs in areas of low or disturbed flow and absent in areas of high flow. In the embryonic heart, high-flow regime applies to the endocardial cushion area, and the absence of cilia here coincides with the process of endothelial-to-mesenchymal transition (EndoMT).
  
  
  OBJECTIVE
  In this study, we investigated the role of the primary cilium in defining the responses of ECs to fluid shear stress and in EndoMT.
  
  
  RESULTS
  Nonciliated mouse embryonic ECs with a mutation in Tg737/Ift88 were used to compare the response to fluid shear stress to that of ciliated ECs. In vitro, nonciliated ECs undergo shear-induced EndoMT, which is accompanied by downregulation of Klf4. This Tgfβ/Alk5-dependent transformation is prevented by blocking Tgfβ signaling, overexpression of Klf4, or rescue of the primary cilium. In the hearts of Tg737(orpk/orpk) embryos, Tgfβ/Alk5 signaling was activated in areas in which ECs would normally be ciliated but now lack cilia because of the mutation. In these areas, ECs show increased Smad2 phosphorylation and expression of α-smooth muscle actin.
  
  
  CONCLUSIONS
  This study demonstrates the central role of primary cilia in rendering ECs prone to shear-induced activation of Tgfβ/Alk5 signaling and EndoMT and thereby provides a functional link between primary cilia and flow-related endothelial performance.
authors.affiliation: Department of Anatomy and Embryology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Anastasia D
authors.initials: AD
authors.lastname: Egorova
authors.forename: Padmini P S J
authors.initials: PP
authors.lastname: Khedoe
authors.forename: Marie-José T H
authors.initials: MJ
authors.lastname: Goumans
authors.forename: Bradley K
authors.initials: BK
authors.lastname: Yoder
authors.forename: Surya M
authors.initials: SM
authors.lastname: Nauli
authors.forename: Peter
authors.initials: P
authors.lastname: ten Dijke
authors.forename: Robert E
authors.initials: RE
authors.lastname: Poelmann
authors.forename: Beerend P
authors.initials: BP
authors.lastname: Hierck
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000502:physiology; D002923:Cilia / Q000473:pathology* / Q000502:physiology*; D042783:Endothelial Cells / Q000473:pathology / Q000502:physiology; D058750:Epithelial-Mesenchymal Transition / Q000502:physiology*; D005786:Gene Expression Regulation / Q000502:physiology; D000090062:Kruppel-Like Factor 4; D051741:Kruppel-Like Transcription Factors / Q000235:genetics / Q000378:metabolism; D040542:Mechanotransduction, Cellular / Q000502:physiology*; D008648:Mesoderm / Q000473:pathology / Q000502:physiology; D051379:Mice; D008817:Mice, Mutant Strains; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism; D051899:Smad2 Protein / Q000378:metabolism; D013314:Stress, Mechanical; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: C498314:Klf2 protein, mouse; C000715468:Klf4 protein, mouse; D000090062:Kruppel-Like Factor 4; D051741:Kruppel-Like Transcription Factors; D018125:Receptors, Transforming Growth Factor beta; D051899:Smad2 Protein; C497783:Smad2 protein, mouse; C490898:Tg737Rpw protein, mouse; D025521:Tumor Suppressor Proteins; D017346:Protein Serine-Threonine Kinases; D000077293:Receptor, Transforming Growth Factor-beta Type I; C000625842:Tgfbr1 protein, mouse